Method of increasing the number of phases of electric currents.



N0. 7|4,637. Patented Nov. 25, I902.

A. a. DAVIS. IETHOU'OF INCREASING THE NUMBER OF PHASES OF ELECTRICCURBENTS.

Ap lication filed Apr. 16, 1902.

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' No; 714,637. Patented Nov. 25, I902.

A. G. DAV|$.,

METHOD OF INCREASING THE NUMBER OF P HASES 0F ELECTRIC CURRENTS.

(Application filed Apr. 16, 1902.; f No Model'.) 2 Sheets-Sheet 2,

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UNITED STATES ALBERT G. DAVIS, OF SCHENECTADY,

PATENT OFFICE.

NElV YORK, ASSIGNOR T,O GENERAL METHOD OF INCREASING THE NUMBER OFPHASES OF ELECTRIC CURRENTS.

SPECIFICATION forming part of Letters Patent No. 714,637, dated November25, 1902.

Original application filed June 25,1897, Serial No. 642.239.

To cold whom it may concern.-

Be it known that I, ALBERT G. DAVIS, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New York, haveinvented certain new and useful Improvements in Methods of Increasingthe Number ofPhases of Electric Currents, (Case No. 2,837,) of which thefollowingis aspecification.

This application is a division of my application Serial No. 642,239,filed June 25,1897.

My invention consists in a novel method of increasing the number ofphases of an alterhating electric current, and is particularly useful inconnection with systems of electrical distribution in which it isdesired to supply multiphase translating devices from singlephase mains.

In practicing my invention I provide a plurality of sources ofelectromotive force-preferably, though not necessarily, counterelectromotive forcedephased from each other by a definite and fixedamount, and I prefer to connect these sources in series across each pairof the mains carrying the current Whose number of phases is to beincreased. The electromotive forces of these sources being dephased fromeach other form with the electromotive force on the mains a system ofpolyphase electromotive forces of an order depending on the number ofphases of electromotive force of the sources and on the order of theoriginal system. For example, it is possible to join two armatures,mechanically or otherwise, so that their electromotive forces aredephased by ninety degrees and to connect them in series across a pairof single-phase mains. With this arrangement a two-phase system ofcurrents and electromotive force may be obtained. In a similar manner itis possible to obtain a three-phase system.

In the annexed drawings, which illustrate apparatus for carrying out myinvention, Figure 1 is a general view of a single-phase system ofdistribution with means for supplying two-phase currents to atranslating device connected thereto. Fig. 2 is a view ofa modification,and Figs. 3 and 4 are vector diagrams.

Referring more particularly to Fig. 1, A

Divided and this application filed April 16, 1902. Serial (No model.)

represents a single-phase generator feeding a pair of mains S 9 throughthe step-up transformer T. Connected to these mains are othertransformers, as T T At those portions of the system where single phasetranslating devices only are desired these transformers are connected toa pair of secondary mains in the usual way. Such an arrangement isillustrated at T where lamps L are shown in multiple with the secondarymains; but at points Where multiphase currents are desired, as at T, Iprovide a novel phasemodifier, by means of which the method constitutingthe subject-matter of this application is carried out. It will be seenthat the mains 4 and 5, leading from the secondary winding of T, areconnected to the primary windings B B of a pair of synchronousdynamo-electric machines connected in series across the lines. Thesemachines are pref- 7o erably motors, but may, if preferred, receiveexternal power. The secondary members C C of these machines, which inthe form shown are the direct-current members, are rigidly coupledtogether, as by the shaft S, in such a way that the electromotive forcesor counter electromotive forces of the two machines are dephased. In theplace of the rigid mechanical connection Imay, of course, make use ofany mechanical or electrical or other means which will secure thedesired result of rigidly maintaining a fixed and definite phaserelation in the counter electromotive forces of the motor-windings. Themembers C C are shown as excited from the direct-current exciter E, andtheir excitation is cont rolled by the adjustable resistances R R asusual.

In the specific form illustrated the phaseangle between theelectromotive forces of the two motors is ninety degrees. Let the Vectored, Fig. 3, represent in magnitude and phase the impressed electromotiveforce at the secondary terminals of T. Let ab and be, two vectors, suchthat the angle abc is ninety degrees, represent the electromotive forceof the two auxiliary machines. Then if the two field-magnets C C areproperly adjusted the vectors ab and be will form with their resultantac an isosceles right triangle, I00

and the resultant may be made equal in magnitude to the impressedelectromotive force ed and opposite in phase. Therefore theeleetromotiveforces ab, be, and do are such that two-phase currents flow in thesystem 4 5 6, connected to the outer terminals and to the pointintermediate the windings.

I have shown various translating devices connected with the mains, asmotors M M M M. M is a three-phase motor fed through thephasing-transformer T This phasingtransformer is of the well-known Scotttype, and need not be particularly described herein. M is a two-phaseinduction-motor of any preferred type. M is a monocyclic inductionmotor,so wound as to take current from the main 6 only when starting, as iswell understood in the art. A synchronous motor may be used, ifpreferred, and I have shown a monocyclic synchronous motor at M,provided with a separate exciter and rh eostat.

High-voltage lamps L may be connected across the mains 4 5, whilelow-voltage lamps L may be inserted, as is usual, in two-phase systems.I have also shown lamps L connected direct to the secondary terminals ofthe transformer T, where they will not tend to unbalance the system.

As indicated in Fig. 4, the angle between the two auxiliary sources ofelectromotive force may be made one hundred and twenty degrees, when athree-phase system will be formed, the vectors being a'b, U0, and de.

It is obvious that by suitably choosing the number and phase-angles ofthe auxiliary sources of electromotive force any preferred system may beobtained.

I have shown the improved phase-modifier, by means of which my presentinvention is carried out, applied to a single-phase system, but it isobvious that it may be applied to any system whatever. Eachphase=modifier so applied will serve to increase the number of phases ofelectromotive force between the two terminals across which it isconnected.

I have illustrated in Fig. 2 another form which the improvedphase-modifier may take. T is a source of electromotive force and may bea transformer connected to a single-phase,

system at any desired point. B B are two angularly-displaced primarywindings, preferably on a single core, connected in series as shown. Cis the secondary member,which may be of any suitable type as, forexample, similar to O or C, Fig. 1. I have, however, shown it as a shorteircuited rotor. When once started, this device will run as asingle-phase induction-motor, but the counter electromotive forces ofthe two windings B and B are dephased, as one winding is in advance ofthe resultant polar line, while one is behind it. The dephased counterelectromotive forces act as do the electromotive forces or counterelectromotive forces of B and B, Fig. 1, and the wires 4: 5 6, connectedto the outer andintermediate terminals of the two windings, form amultiphase system, the phase-angles of which depend on the anglesbetween the connection B and B In order to start the armature 0 I haveillustrated a condenser K with a suitable switch S in multiple with oneof the inducingwindings, as B When the switch S is closed, thiscondenser tends to advance the current in B with which it is in series,and to lag the current in B with which it is in shunt, and a rotaryfield is created, which causes the armature to start. When a properspeed is attained, the switch S is opened and the machine runs as aninduction-motor, as before stated, supplying multiphase currents to themains 4t 5 6.

Although I have shown in the present application various forms of aphase-modifier by means of which my invention may be practiced, it willbe evident that my invention is not restricted to any particularapparatus.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. The method of increasing the number of phases of an electric currentfrom a source of alternating electromotive force, which consists inopposing an electromotive force from said source by the resultantelectromotive forces of a plurality of sources, and rigidlymaintainingfixed the relative phase relations of the componentelectromotive forces going to make up the said resultant, substantiallyas set forth.

2. The method of changing single-phase current to multiphase, whichconsists in supplying said current to a plurality of motorwindingsconnected in series, maintaining by external means a fixed and definitephase relation between the counter electromotive forces of themotor-windings, and taking off dephased currents due to variouselectromotive forces of the resulting system.

In witness whereof I have hereunto set my hand this 15th day of April,1902.

ALBERT G. DAVIS.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD.

